In many seats for vehicle, a various angular and positional adjusting mechanisms are provided in order to fit with the respective figure and driving posture of sitting passengers. Particularly, a seat rail apparatus allowing a driver to adjust the forward/backward position of the seat to an optimum point for operating the pedal, is the most basic seat adjusting mechanism, and are mounted on almost driver's seats (and passenger seats) of vehicles.
In such seat rail apparatus, a power driven type, which is driven by the power of an electric motor, and a manual type, which requires manual operation by a passenger seating thereon, are available. Particularly, compared to the powered type, the manual type seat rail apparatus has the following advantages; i.e., because of simple structure, low risk of failure, light in weight and low in manufacturing cost, many vehicles adopt manual type seat rail apparatus.
Conventionally, as the seat rail apparatus of the manual type, the following type has been often adopted. That is, an upper rail fixed to the seat cushion side and a lower rail member fixed to the floor face side of a body of the vehicle are provided; and an engagement section having a “saw teeth-like” configuration is provided in the longitudinal direction of the upper rail, and an engagement member capable of arbitrarily engaging with and disengaging from the engagement section is provided to the lower rail member side; thus the locking is achieved in a stepless manner.
On the other hand, recently, there has been proposed the following system. That is, a “screw (shaft)” and a “nut”, which have a lead angle larger than the angle of friction respectively, are disposed between an upper rail and a lower rail members, and when a passenger applies a load to a seat in the forward/backward direction in the unlocked state, the seat can be slid forward/backward. According to the seat rail apparatus of such system, the rotation of the screw can be arbitrarily locked and the forward/backward position of seat for vehicle is adjustable in a stepless manner accordingly. Such seat rail apparatus are disclosed in the patent document 1 and patent document 2.
The seat rail apparatus set forth in the Japanese Laid-Open Patent Application 11-115570/1999 (patent document 1) is provided with an inertia member, which rotates integrally with a nut, at the substantially central portion of the nut provided within the seat rail apparatus, and a lock mechanism capable of locking the rotation of the nut via the inertia member on the lower face of the lower rail member. The lock mechanism has a locking member and is arranged so that a lock pin protruding on an upper part of the locking member is brought into a friction engagement with the inertia member through the lower rail member; and thus the rotation of the inertia member is locked at an arbitrary position. Therefore, it is arranged so that, when the rotation of the inertia member is locked, the rotation of the nut, which integrally rotates with the inertia member, is also locked; and thus, the slide of the seat rail is fixed at an arbitrarily position.
Also, the seat rail apparatus set forth in the patent document 1 is provided with an emergency lock for preventing the seat from moving in the forward/backward direction when an excessive impact load is applied to the vehicle in a state the lock pin is disengaged from the inertia member (in a state the seat rail is unlocked). The emergency lock is arranged so that, when a screw rotates exceeding a predetermined value, a roller is expanded, and the roller is sandwiched in a narrow portion formed between a roller guide and the nut, and the rotation of the nut can be locked by means of the friction engagement with the roller; thus the seat rail is locked.
The emergency lock is a mechanism, which locks the rotation of the screw only in one direction of clockwise or counterclockwise. Therefore, in order to cope with any case of collision at the front or back, the lock mechanisms are provided at the front and back of the nut. When the emergency lock is functioned, a passenger operates to apply a load via the seat in the direction opposite to the load applied to the upper rail member; then, the nut rotates in the opposite direction and the roller is pulled out from the narrow portion; and thereby the lock is released.
In the seat rail apparatus set forth in the Japanese Laid-Open Patent Application 2000-343989/2000 (patent document 2), the front-end portion of a screw is coupled with a lock mechanism provided to an upper rail member. In this seat rail apparatus, the screw provided with a brake ring at the front end thereof is coupled with the lock mechanism having a locking member and a brake drum attached to an end portion of the upper rail member, and it is arranged so that, when a lock pin provided to the locking member makes a friction engagement with the brake ring, the rotation of the screw is locked.
According to the seat rail apparatus set forth in the patent document 1 and the patent document 2, since the lead angle of the nut and the screw is formed larger than the angle of friction, when a passenger applies a force to the seat in the forward/backward direction, the screw rotates and the seat can be slid. And only by locking the rotation of the screw, the seat can be fixed at an appropriate position; thus, “slide and lock in a stepless manner” is achieved.
However, there is a disadvantage in the seat rail apparatus set forth in the patent document 1 and the patent document 2 such that, since an arrangement to lock the rotation of the screw by means of the friction between the lock pin and the brake ring or the inertia member is employed, a large load accts on the respective members when locking the rotation of the screw and a play is easily generated.
Particularly, the emergency lock mechanism disclosed in the patent document 1 is a mechanism such that the screw is rotated with a load larger than a predetermined value, which is capable of locking only the rotation in one direction; i.e., clockwise or counterclockwise direction. To cope with the case where a load larger than the predetermined value is applied due to a collision at the front/back, the emergency lock mechanism has to be provided at the both sides of the nut to cope with the cases of collision from the respective directions. When such arrangement is adopted, the apparatus itself becomes larger in size, the number of the component parts becomes larger, and further, the structure thereof becomes complicated resulting in a disadvantage in the aspect of manufacturing cost and efficiency.
Also, when the emergency lock disclosed in the patent document 1 has functioned, in order to release the emergency lock, a passenger has to operate to apply a load in the direction opposite to the direction of the applied load. Therefore, there is a disadvantage such that, when the passenger operates the emergency lock erroneously, the emergency lock cannot be easily unlocked. It is required that the interior components of vehicle naturally guide a passenger to a proper operation without reading user's manual. The present invention has been proposed to solve the above problems, and an object thereof is as described below.
[Patent document 1] Japanese Laid-Open Patent Application 11-115570/1999
[Patent document 2] Japanese Laid-Open Patent Application 2000-343989/2000